The Determination of Fat by fjzhangxiaoquan


									                      Lab Activity 10a
                  The Determination of Fat
               in Potato Chips and Hot Dogs
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Fat, sugar, and salt are three food components that worry nutritionists and provide copy
for newspaper editors because Americans tend to consume too much of these food
ingredients. In this experiment you will measure the amount of fat in some foods that
could be part of a typical fast food meal. Two approaches will be used to determine the
fat content of foods. In fat-coated foods such as potato chips or French fries, the fat can
simply be dissolved out of the food using a solvent. However, another approach must
be used for fat in meat products (such as hot dogs) because the fat is bound up in
animal tissue (protein). Therefore, the meat must be chemically treated to break down
the protein and other tissues in order to liberate the fat. Since the liberated fat can float
on water, it can be easily removed and weighed.

Science Processes to be Used:

      Quantitative lab skills
      Qualitative lab skills
      Analysis of fat in potato chips
      Analysis of fat in hot dogs

       4 grams of chips
       50 mL of petroleum
       mortar and pestle
       glass funnel and a funnel support
       2 sheets of filter paper to fit the funnel
       2 50-mL beakers
       hot plate or steam bath
       4 grams of ground hot dog meat or other meat sample
       250 mL beaker
       10 mL of "protein liquefying reagent"
       2 test tubes
       2 50-mL beakers
       2 long-stem glass Pasteur pipets
       Pipet bulb

                       Activity 1: Fat in Potato Chips
The essential procedure is very simple: petroleum ether (a commercial mixture of
hydrocarbons that is widely used as a solvent) is mixed with ground-up chips to extract
the fat. After separating the solvent mixture from the chips, the petroleum ether is
allowed to evaporate, leaving behind the fat, which can then be weighed. The essential
steps are as follows:
        1. Obtain two weighed samples of potato chips or other snack chips.
        2. Grind up the samples and mix them with petroleum ether to extract the fat.
        3. Separate the petroleum ether from the potato chips by filtration into a weighed
        4. Evaporate the petroleum ether on a steam bath or hot plate.
        5. Weigh the beaker and calculate the mass of fat by difference.
        6. Calculate the percent fat in the chips.

Detailed Procedure
This procedure will be done twice, using two samples of chips.
       1. Obtain two small beakers that are clean and dry. Label them with identifying
          numbers (1 and 2).

       2. Accurately weigh out two samples of chips of about 2-3 grams each. This is
          done most conveniently by using small sheets of paper or small plastic
          weighing dishes. Record the weight of the first paper or dish to the nearest
          0.01 gram, add 2-3 grams of chips, and again record the weight to the
          nearest 0.01 gm. Repeat with the second sample. Keep track of which
          sample is which.

       Reminder about weighing: It is important to check the balance each time it is
       used to be sure it reads 0.00 g when there is nothing on the balance pan.

       3. Also weigh the two beakers and record their weights to the nearest 0.01
          gram. (First check to be sure that the balance reads 0.00 g when empty.)

       4. Put chip sample #1 in a clean porcelain mortar and use a pestle to crush the
          chips into very small pieces. (Because of the fat, the mixture may be rather
      5. Add 15 mL of petroleum ether to the mortar and grind the mixture thoroughly.

      6. Prepare a glass funnel with folded filter paper. Mount it over weighed beaker
         #1. Using a spatula, carefully transfer the potato chip mixture into the filter.
         Try to get most of the mixture into the filter.

      7. In order to rinse out any remaining fat in the mortar and on the chip mixture,
         add 5 mL more petroleum ether to the mortar. Stir it around with the pestle,
         then poor it onto the chip mixture in the filter.

      8. Repeat with another 5 mL rinse of the mortar and the chip mixture in the filter.

      9. Repeat steps 4-8 with the second sample of chips using the same mortar and
         pestle, but a fresh piece of filter paper and weighed beaker #2.

      10. When both mixtures have finished filtering, the next step is to remove all of
         the petroleum ether by evaporation. There are two ways this can be done.
            a. You can leave the beakers in a well-ventilated place (such as outside,
                if you know it's going to be a nice day until the next day, by which time
                the solvent will have evaporated.
            b. A much faster way is to place the beakers in a steam (water) bath or
                hot plate (ie, electric range top on "low" or "warm" settings) with the
                vent on (this only works if your vent actually vents to the outside).
                Leave them for about 15 minutes or until all of the petroleum ether has
                evaporated. Then remove the beakers from the steam bath or hot
                plate, carefully wipe the outsides to remove all water, and let them cool
                for a few minutes.

      11. Re-weigh the beakers and record the weights to the nearest 0.01 gram. (First
         check to be sure the balance reads zero when empty.)

      For each sample, calculate by subtraction the mass of chips and the mass of fat.
      Then calculate the percent fat in the chips:

                    % fat = mass of fat mass of chips x 100
                                 mass of chips

                         Activity 2: Fat in a Hot Dog
This procedure is written for hot dogs but it can be used for any kind of meat sample.
For example, you may wish to investigate whether different brands of hot dogs differ
significantly in fat content, whether chicken or turkey hot dogs differ from beef and pork
hot dogs, whether hot dogs and hamburgers differ significantly in fat, whether "low fat"
products are really as claimed, and how vegetarian hot dogs compare to meat hot dogs.
The experimental procedure utilizes a special solution identified simply as "protein
liquefying reagent." This is a highly alkaline mixture containing sodium hydroxide,
sodium salicylate, potassium sulfite, isopropyl alcohol, and water. The essential steps
are as follows: 1. Obtain a sample of ground hot dog or other meat. 2. Determine the
masses of two separate hot dog samples in test tubes. 3 . React the hot dog meat with
protein liquefying reagent. 4. Cool and separate the samples. 5. Remove the fat layer
from each hot dog sample and weigh it. 6. Calculate the percent fat in a hot dog.

Detailed Procedure
   1. Put approximately 75 mL of water in a 250 mL beaker. Place the beaker of water
       on a hot plate (ie, electric range top on "low" setting) and heat the water to
       between 80 and 90˚C.
   2. While the water is heating, obtain two test tubes and label them #1 and #2. Put
       the labels high on the tubes near the top. Check to be sure that the empty
       balance reads exactly 0.00 g, then weigh the test tubes and record their weights
       to the nearest 0.01 gram.
   3. Put between 2 and 2.5 grams of ground hot dog meat in each test tube and re-
       weigh the tubes. Record the weight of each tube + hot dog sample to the nearest
       0.01 gram.
   4. Add about 5 mL of the protein liquefying reagent to each hot dog meat sample.
   5. Put the test tubes in the beaker of water and heat the beaker on a hot plate until
       the reagent in the tube starts to boil (about 80˚C). Maintain the temperature of
       the water so that the contents of the test tubes boil for 10 minutes. Do not leave
       the beaker and test tubes unattended. The liquid could boil out of the test tube.
   6. After the mixture has boiled for 10 minutes, it should be dark brown with some
       yellow fat floating at the top. Remove the test tubes from the hot water, stand
       them in a 250 mL beaker, and let them stand until they are cool enough to
       handle. Do not let them cool completely because the fat may turn from liquid to
   7. Label two small containers (50 mL) beakers, or vials, test tubes, or watch
       glasses) as "sample 1" and "sample 2," and then weigh them to the nearest 0.01
       gram. (Remember to check first to be sure the balance reads 0.00 g when
       empty.) Record the masses on the data sheet.
   8. Use a Pasteur pipet (glass tube with a long thin stem and a small rubber bulb
       attached to the top) to slowly transfer the top fat layer from test tube #1 to the
       correct pre-weighed container. Be very careful to remove all of the fat but none of
       the brown liquid. Work slowly: it takes patience to do this correctly so that only
       the fat is removed. If you accidentally suck up some of the brown liquid, it can
       usually be removed from the bottom of the container of fat, using the Pasteur
   9. Repeat the procedure for the other sample.
   10. Weigh the containers of fat to the nearest 0.01 gram and record their weights in
       the data table.
By subtraction of weights in the data table, calculate the mass of hot dog and the mass
of fat for each sample. The percent fat is then calculated from the relationship:

                              % fat = mass of fat x 100
                                    mass of hot dog

Safety Notes and Disposal
   1. Activity 1 uses petroleum ether, a gasoline-like solvent that is extremely
      flammable. Therefore it is absolutely essential that no open flames be present
      anywhere in the laboratory during this experiment. Under no circumstances
      should the heating be done with a Bunsen burner.
   2. Safety glasses are essential to prevent possible injury from any splashed
   3. In Activity 2, do not allow the protein liquefying reagent to contact your skin. It is
      highly caustic and can cause serious skin damage.
   4. Check that there are no open flames near you as you work since the
      protein liquefying reagent is flammable.
   5. Heat the samples ONLY on a hot plate. Do NOT use an open flame. The vapor
      from the protein liquefying reagent is extremely flammable.
   6. Cleanup: The "brown protein liquid" remaining in the test tubes can be washed
      down the drain with plenty of water. The fat portions, filter paper, etc., can be
      thrown in the trash.

Your grade will be determined by your data, accuracy, calculations, and answers to the
post-lab questions.

Post-Lab Questions

Fill in the following chart for the percent fat in potato chips or tortilla chips (for 2
samples), then answer the questions that follow.

                                      Sample 1                 Sample 2
   Brand of chips
   Mass of dish + chips
   Mass of empty dish
   Mass of chips
   Mass of beaker + fat
  Mass of empty beaker
  Mass of fat
  Percent fat in chips

   1. Looking at the your results, can you make any generalizations? For example, do
      potato chips have more or less fat than tortilla chips? If your class analyzed any
      "low fat" products, do the results support this claim?
   2. A snack pack of potato chips or other kinds of chips holds one ounce (28 grams)
      of chips. Based on your data, how much fat is present in a snack pack? In such a
      bag of chips there are about 15 grams of carbohydrate and about 1 gram of
      protein. Given that carbohydrates and protein provide about 4 Calories of energy
      per gram and fats provide about 9 Calories per gram, what is the energy
      equivalent (in Calories) of bag of chips? What percent Calories are from the fat?
   3. Suppose you wished to use potato chips as a major source of protein in your
      diet. How many 1 ounce (28 grams) bags of potato chips would you have to eat
      to satisfy the recommended minimum daily allowance for protein (60 grams for a
      typical young adult)? How many grams of fat are in this amount of potato chips?


Fill in the following chart for the percent of fat in a hot dog (or other meat product) (for 2
samples), then answer the questions that follow.

                                     Sample 1                Sample 2
  Description of the sample
  Mass of test tube + hot dog
  Mass of empty test tube
  Mass of hot dog
  Mass of container + fat
  Mass of empty container
  Mass of fat
  Percent fat in hot dog

   1. If you analayzed different kinds of hot dogs or other meats, what can you
      conclude about the fat content in these products? Are some products significantly
      lower in fat than others?
   2. A typical hot dog weighs about 45 grams. Using your data, calculate the number
      of grams of fat in the hot dog you analyzed. There are about 7 grams of protein in
      a hot dog. Almost all of the remaining mass is water. Calculate how many
   Calories are provided by the fat, by the protein, and by the water. What
   percentage of the Calories in the hot dog can be attributed to the fat?
3. If hot dogs sell for $2.29 a pound, what is the cost per pound of protein in hot
4. Examine the labels on two kinds of "lean" cold cuts at make claims such as "93%
   fat free." Using the information on the label, calculate the fat content in terms of
   the percent of the total Calories provided by the fat.

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